U.S. patent number 4,031,286 [Application Number 05/661,331] was granted by the patent office on 1977-06-21 for fluorocarbon polymer coating compositions containing mica particles.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Herman Ernest Seymus.
United States Patent |
4,031,286 |
Seymus |
* June 21, 1977 |
Fluorocarbon polymer coating compositions containing mica
particles
Abstract
Aqueous fluorocarbon polymer coating compositions which contain
colloidal silica and mica particles are provided. These
compositions are useful for coating substrates, especially metallic
cookware and bakeware to give non-stick finishes having improved
resistance degradation by hot oil.
Inventors: |
Seymus; Herman Ernest (Lint,
BE) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
[*] Notice: |
The portion of the term of this patent
subsequent to July 20, 1993 has been disclaimed. |
Family
ID: |
27016878 |
Appl.
No.: |
05/661,331 |
Filed: |
February 25, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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400040 |
Sep 24, 1973 |
3970627 |
|
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|
Current U.S.
Class: |
428/324; 428/328;
428/331; 428/432; 428/454; 428/463; 428/469; 524/449 |
Current CPC
Class: |
A47J
36/02 (20130101); C08K 3/346 (20130101); C08K
3/346 (20130101); C08L 27/12 (20130101); Y10T
428/31699 (20150401); Y10T 428/256 (20150115); Y10T
428/259 (20150115); Y10T 428/251 (20150115) |
Current International
Class: |
A47J
36/02 (20060101); C08K 3/34 (20060101); C08K
3/00 (20060101); B32B 005/16 (); C08L 027/18 ();
B32B 015/08 () |
Field of
Search: |
;428/324,422,331,328,428,432,454,463,471,469 ;260/29.6F |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Robinson; Ellis
Claims
What is claimed is:
1. An aqueous coating composition consisting essentially of:
a. about 40-93%, by weight of the total of (a), (b) and (c) solids,
of a particulate fluorocarbon polymer,
b. about 5-35%, by weight of the total of (a), (b) and (c) solids,
of colloidal silica stabilized with sodium ions, having a particle
size of 7-25 millimicrons, a specific surface area of 125-420
square meters per gram, a silica content of 30-50% by weight, and a
pH of 8.4-9.9 at 25.degree. C., or a mixture of said silica with
water-soluble alkali metal silicate, in a ratio in the range
between 75:25 and 10:90 by weight respectively,
c. about 2-25%, by weight of the total of (a), (b) and (c) solids,
of irregularly shaped mica platelets 80% of which are 0.05-0.15
micron thick and 4-50 microns wide (longest dimension) and
d. water as a carrier.
2. The composition of claim 1 wherein the fluorocarbon polymer in
(a) is polytetrafluoroethylene.
3. The composition of claim 1 wherein the solids of (a), (b) and
(c) comprise about 50-90% by weight (a), about 10-20% by weight (b)
and about 5-15% by weight (c).
4. The composition of claim 1 wherein the polymer in (a) is PTFE
and the colloidal silica in (b) is one whose particles are
surface-modified with aluminum, having a particle size of 13-14
millicrons, a specific surface area of 210-230 square meters per
gram, a silica content of 30% and a pH at 25.degree. C of 9.0.
5. An article bearing a fused coating of the composition of claim
1.
6. An article bearing a fused coating of the composition of claim
2.
7. An article bearing a fused coating of the composition of claim
3.
Description
BACKGROUND OF THE INVENTION
l. Field of the Invention
This invention relates to aqueous fluorocarbon polymer coating
compositions and articles coated therewith and more particularly to
such compositions and metallic articles coated therewith having
improved resistance to degradation by hot oil.
2. Prior Art
In recent years, the use of fluorocarbon polymer coatings as
non-stick finishes for metal substrates, particularly for cookware,
has become widespread. The physical nature of fluorocarbon polymers
make it difficult to bond them to metallic substrates sufficiently
well to prevent coatings of the polymers from blistering and
peeling during use. This is especially true of
polytetrafluoroethylene.
Adhesion of such coatings has been improved by the addition of a
water-soluble alkali metal silicate or a colloidal silica to the
fluorocarbon polymer coating composition, as described in U.S. Pat.
No. 2,825,664, issued Mar. 4, 1958 to James R. Huntsberger. In U.S.
patent application Ser. No. 405,798 filed Oct. 12, 1973, adhesion
of such coatings was improved by adding colloidal silica stabilized
with sodium ions to the fluorocarbon polymer coating
composition.
While the compositions described in the aforesaid references do
improve adhesion to unprimed metal substrates, there are some
end-use applications where resistance to degradation by hot oil is
desirable. In cookware, for example, resistance to degradation by
hot oil, especially at about 200.degree. C, is desirable in such
articles as frypans, meat grills and sauce pans, where fats and
oils are in contact with the fluorocarbon polymer coating during
the cooking process.
SUMMARY OF THE INVENTION
According to the present invention there is provided an aqueous
coating composition comprising:
A. ABOUT 40-93%, BY WEIGHT OF THE TOTAL OF (A), (B) AND (C) SOLIDS,
OF A FLUOROCARBON POLYMER,
B. ABOUT 5-35%, BY WEIGHT OF THE TOTAL OF (A), (B) AND (C) SOLIDS,
OF COLLOIDAL SILICA STABILIZED WITH SODIUM IONS, OR A MIXTURE OF
SAID SILICA WITH A WATER-SOLUBLE ALKALI METAL SILICATE,
C. ABOUT 2-25%, BY WEIGHT OF THE TOTAL OF (A), (B) AND (C) SOLIDS,
OF MICA PARTICLES, AND
D. WATER AS A CARRIER.
There is also provided an article comprising a substrate coated
with a fused coating of the above-described coating composition.
These fused coatings have improved resistance to degradation by hot
oil.
DETAILED DESCRIPTION OF THE INVENTION
The fluorocarbon polymers used in the compositions are of
hydrocarbon monomers completely substituted with fluorine atoms.
Illustrative of such polymers ae polytetrafluoroethylene (PTFE),
copolymers of tetrafluoroethylene and hexafluoropropylene in all
monomer unit ratios, and fluorochlorocarbon polymers such as
polymonochlorotrifluoroethylene. Mixtures of these can be used.
PTFE is preferred.
The fluorocarbon polymer used is particulate. The particles are
preferably small enough to pass through the nozzle of a spray gun
without clogging it and small enough to give the resulting film
coalescence and integrity. In ordinary situations, the particles
are preferably no larger than about 0.35 micron (average) in the
longest dimension.
Although one can use a dry flour or powder of fluorocarbon polymer
and provide a liquid carrier separately, it is preferred to use the
polymer in the form of an aqueous dispersion because it is most
easily obtained on the market in that form. A dispersion of
fluorocarbon polymer in an organic liquid miscible with water, such
as ethanol, isopropanol, acetone or a Cellosolve, can also be used.
In any case, the liquid also serves as a portion of the carrier for
the composition.
The fluorocarbon polymer is present in the composition at a
concentration of from about 40% through about 93%, by weight of the
total of fluorocarbon polymer, mica and colloidal silica solids. A
concentration of 50-90% is preferred; 70-90% is even more
preferred.
The colloidal silica used in the composition is generally in the
form of an aqueous sol. This silica is stabilized with sodium ions,
has a particle size of 7-25 millimicrons, a specific surface area
of 125-420 square meters per gram, a silica content (calculated at
SiO.sub.2) of 30-50% by weight, and a pH of 8.4-9.9 at 25.degree.
C. Typical of such a colloidal silica are those sold by E. I.
duPont de Nemours and Company as "Ludox HS-40", "Ludox-HS", "Ludox
LS", "Ludox SM-30", "Ludox TM", and "Ludox AM". Mixtures of silicas
can be used. "Ludox AM" is preferred. This product is a sodium
stabilized colloidal silica whose particles are surface-modified
with aluminum, having a particle size of 13-14 millimicrons, a
specific surface area of 210-230 square meters per gram, a silica
content (calculated as SiO.sub.2) of 30.0% and a pH at 25.degree. C
of 9.0.
The colloidal silica is present in the composition at a
concentration of from aout 5 through 35%, preferably 10-20%, by
weight of the total of fluorocarbon polymer, mica and silica
solids. Instead of colloidal silica, a mixture of colloidal silica
and a water-soluble alkali metal silicate can be used, as described
in U.S. Pat. No. 2,825,664, the disclosure of which is hereby
incorporated by reference.
As described in U.S. Pat. No. 2,825,664, any aqueous solution of an
alkali metal silicate or mixtures thereof may be used in the
compositions of this invention. Such silicate solutions are
available commercially in a wide range of SiO.sub.2 alkali metal
oxide molar ratios, e.g., from about 1:1 to 4:1. Certain
water-soluble alkali metal silicates having an SiO.sub.2 molar
proportion above 4 can be prepared and may also be used. Examples
of suitable water-soluble alkali metal silicates are potassium
silicate, sodium silicate and lithium polysilicate. The ratio of
alkali metal silicate to colloidal silica is usually in the range
between 25:75 and 90:10 by weight, preferably between 50:50 and
80:20 by weight.
The mica used in the compositions of this invention is of the wet
ground variety and is provided in the form of irregularly shaped
platelets, 80% by weight of which are about 0.05-0.15 micron thick
and about 4-50 microns wide in the longest dimension. Such micas
are available commercially. The mica is generally present in a
composition of the invention at a concentration of about 2-25%, by
weight, of the total of fluorocarbon polymer, mica and silica
solids, preferably 5-15% by weight. Mixtures of two or more types
of mica having different particle size ranges can also be used.
The composition itself is made by simply mixing proper amounts of a
suitable colloidal silica sol., with or without an alkali metal
silicate, mica or coated mica and a suitable fluorocarbon polymer
dispersion. A minimum of shear should be used in preparing the
composition so that the shapes and sizes of the mica particles are
not altered significantly. The composition can be pigmented, if
this is desired, by first preparing a suitable pigment dispersion
according to any conventional technique and then adding this
pigment dispersion to the silica sol-mica fluoropolymer
mixture.
Adjuncts such as flow agents, coalescing aids, anti-cratering
agents, anti-mudcracking agents and the like can also be added if
this appears necessary.
The resulting composition can be applied by spraying, brushing,
roller-coating, dipping or the like. If the substrate is metal,
this is preferably pre-treated by gritblasting, by the flame
spraying of a metal or a metal oxide, or by frit coating, although
the composition can be applied successfully to phosphated and
chromated non-grit blasted metals. If the substrate is glass, it is
preferably first gritblasted or frit coated.
The composition is ordinarily applied to a thickness of 5-65
microns (dry). After application, the composition is air-dried and
the article baked for a time and at a temperature sufficient to
fuse the fluoropolymer used.
The composition is most useful for coating cookware, especially
bakeware, frying pans, and for coating meat grills, but it can also
be used to coat any article capable of withstanding the baking
temperature used. For example, the composition can be used to coat
bearings, valves, wire, metal foil, boilers, pipes, ship bottoms,
oven liners, iron soleplates, waffle irons, ice cube trays, snow
shovels and plows, chutes, conveyors, dies, tools such as saws,
files and drills, hoppers, and industrial containers and molds. It
can also be used to coat plastic articles.
The invention can be further understood by the following example,
in which all parts and percentages are by weight unless otherwise
indicated.
______________________________________ A coating composition was
prepared by mixing the following ingredients: Parts
______________________________________ Aqueous
polytetrafluoroethylene 67.4 dispersion.sup.1 Sodium lauryl alcohol
sulfate 3.5 dispersing agent (30% in water) Mica (wet ground)
particle size 5.1 distribution between 5 and 30 mircons Carbon
black/aluminum silicate 5.0 dispersion (30% in water, 20% carbon
black and 10% aluminium silicate) Colloidal silica stabilized with
19.0 sodium.sup.2 100.0 ______________________________________
.sup.1 The dispersion contained 60% colloidal
polytetrafluoroethylene and 3.5% octylphenyl polyglycol ether.
.sup.2 The aqueous colloidal silica contained 30% silica stabilized
with sodium, had a SiO.sub.2 /Na.sub.2 O ratio of 230, a particle
size of 13-1 millimicrons and the silica particles surface-modified
with aluminate ions. The PTFE to SiO.sub.2 ratio in this example
is: 100/14.
One coat of this composition was sprayed, to a thickness of 15
microns, on an aluminum panel which had been pre-treated by
grit-blasting to a profile of 10 to 15 microns. The panel was then
baked at 400.degree. C for 10 minutes.
The panel was then boiled in vegetable oil for 3 hours.
Adhesion of the coating to the substrate was determined as
follows:
1. The coating was scratched with a knife down to the metal surface
to give a grid of 10 .times. 10 squares with the lines 2 mm.
apart.
2. An adhesive tape was applied over the grid and then pulled
off.
3. The number of squares remaining was then determined on a
percentage basis. The minimum acceptable level is 70%.
As a control, a duplicate panel was similarly coated with the same
composition lacking the mica component.
The results were as follows:
Control panel; 60% adhesion
Example panel; 80% adhesion.
* * * * *